This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Helicobacter pylori commonly infects the stomach, where it sometimes causes peptic ulcer disease or gastric cancer. H. pylori attachment to the gastric epithelium is mediated by a large family of outer membrane proteins (OMPs), the best studied of which is BabA. Patients infected with strains that express it are more likely to develop peptic ulcer or gastric cancer. A closely related protein, BabB, shows extensive homology with BabA, but its function is unknown. We recently showed that H. pylori strains recovered from experimentally infected macaques had lost expression of BabA. In some cases the babA gene was replaced by babB and in other cases the babA gene was not expressed due to phase variation. Strains lacking BabA expression did not adhere to the Leb blood group antigen that is expressed on rhesus gastric epithelium. We hypothesize that modifications in H. pylori OMP expression represent a remodeling of the bacterial surface so as to avoid host immunity or promote attachment to the gastric epithelium. These studies of BabA and BabB will contribute to ongoing translational research that seek to investigate the use of BabA and BabB as vaccine candidates, and also may have broad implications for the role of genome diversity in promoting chronic infection with H. pylori.